1. Field of the Invention
This invention relates to parallel rings, ring extensions, and phase leads connected thereto, and more particularly, to means for supporting the parallel rings and ring extensions.
2. Description of the Prior Art
Stator windings on large dynamoelectric machines such as turbine generators are disposed on generally cylindrical stator cores. The stator winding on multi-phase generators includes a plurality of phase zones each of which constitute a plurality of coil sides. All the coil sides in each phase zone except those constituting the terminal coil side portions are serially connected at each axial end of the stator core. The unconnected ends of the terminal coil sides constitute terminals which are radially separated from the stator core's axis by discrete radial distances at a first axial end of the stator core.
Parallel conductor ring structures are disposed at the first axial end of the stator core and include a plurality of parallel rings and ring extensions connected thereto at selected circumferential locations. The rings are circumferentially situated about the stator core and the ring extensions protrude generally radially inwardly and axially toward the first end.
The stator and parallel ring structures are enclosed in a casing structure which includes a cylindrical, thin-walled member which has axial gussets connected thereto on the radially inner side. Use of axial gussets with a cylindrical member permits use of a thin-walled member rather than a thick-walled member and thus provides economic advantages thereover.
The parallel rings and ring extensions were supported by a bracing structure at the axial gussets due to the relatively high rigidity and structural support provided by the gussets as compared to the cylindrical members.
Phase leads connect the coil terminals to the appropriate parallel ring extensions. While the circumferential locations for the ring extensions were chosen to correspond to the axial gusset nearest the connected coil terminal, the circumferential locations of the terminals and associated phase leads were dictated by the number of phases, stator winding technique, and the stator's cooling paths. Since the circumferential locations of the coil terminals were seldom the same as the circumferential locations of the ring extensions, the phase leads connecting the terminals and ring extensions were of several lengths necessitating the custom design and manufacture of the phase leads on each machine. As such, each phase lead length required dynamic testing to avoid operational resonance and ensure adequate support therefor.
The bracing structure for the parallel rings must be capable of withstanding forces of up to 1500 pounds per inch for two-pole generators and 2000 pounds per inch for four-pole generators during sudden short circuits between parallel rings in addition to radial forces due to these shorts. Additionally, the bracing system must be capable of supporting its own weight as well as steady state forces in the axial and radial directions. The parallel rings have, heretofore, been clamped between epoxy laminate glass blocks which are custom made for each machine and bracing location. The glass blocks are mounted axially between the parallel rings and are used as spacers on both axial extremes thereof to provide the desired spacing. The spacing, clamping blocks and separated parallel rings were disposed axially between a stopping structure and a bolt-washer assembly and radially against the axial gussets. The bolt-washer assemblies enable selected axial clamping pressures to be applied to the separated parallel rings. However, support against radial forces exerted on the parallel rings and their weight was provided only from friction between the glass epoxy blocks and the parallel ring's external insulation material. Since friction alone was relied upon to provide the radial support necessary to prevent radial motion of the parallel rings, any radial displacement of the rings provided a possibility of abrasion and wear of the parallel ring's insulation and spacing blocks.
Each ring extension's axial traversal of the circumferentially disposed parallel rings facilitated the mechanical interconnection of each ring extension with the adjacent parallel rings so as to stiffen the ring extension. However, since the parallel rings were not positively restrained in the radial direction, the ring extensions, likewise, were not secured in the radial direction.
The lack of positive radial bracing of the parallel rings and ring extensions can reduce the reliability of the utilizing machine. The custom designed phase leads on each machine resulted in higher engineering, manufacturing, and assembly cost and relatively low availability of replacement phase leads for maintenance and/or refurbishment.